[Haskell-cafe] MTL vs Free-monads, what are your experiences

[Damian Nadales]

BTW, when making the distinction between simple and easy I was
referring to this talk:
    https://www.infoq.com/presentations/Simple-Made-Easy

So when I say I would prefer a simple approach, I say that I won't
mind having to spend one month to understand it, as long as I can
write "sustainable programs" (reasonably efficient, extensible,
maitainable, robust, etc).

On Wed, Oct 19, 2016 at 3:13 PM, Alexey Raga <alexey.raga at gmail.com> wrote:
> Working with stacks like "ReaderT AppConfig (StateT AppState IO)" may be
> hard, but using MonadIO, MonadState, MonadReader etc. is much simpler.
>
> This session explains it well: https://www.youtube.com/watch?v=GZPup5Iuaqw
>
> I haven't yet tried Oleg's approach with Freer monads and extensible effects
> though, it looks very interesting. Especially when creating new types of
> effects because writing an "interpreter" seems easier than writing something
> like "MyEffectT / MyEffectMonad" and giving it all the required instances.
>
>
> On Wed, Oct 19, 2016 at 11:57 PM David McBride <toad3k at gmail.com> wrote:
>>
>> I'll say that this conversation caused me to rewrite some networking code
>> I had written in a free monad as mtl.  It is faster and simpler, right?  But
>> transformer stacks with all their typeclasses are really hard to work with
>> and I don't think it was worth it in the end.
>>
>> On Wed, Oct 19, 2016 at 8:29 AM, Damian Nadales <damian.nadales at gmail.com>
>> wrote:
>>>
>>> I was thinking, besides the evaluation of performance, the simplicity
>>> of the approach is also important ("developer time is more expensive
>>> than CPU time" anyone?). Note that I said simple and not easy ;)
>>>
>>> I guess this aspect is a rather subjective one, but maybe there are
>>> elements that can be intuitively quantified. Right now I'm playing
>>> with free monads and MTL, to have an idea which one seems simpler to
>>> me.
>>>
>>>
>>>
>>> On Mon, Oct 17, 2016 at 8:06 PM, Julian <hasufell at hasufell.de> wrote:
>>> > On 15/10/16 15:49, Joachim Breitner wrote:
>>> >> Hi,
>>> >>
>>> >> Am Freitag, den 14.10.2016, 17:35 +0200 schrieb Damian Nadales:
>>> >>> Do you have
>>> >>> any experience using any of these approaches. If so would you mind
>>> >>> sharing? ;)
>>> >>
>>> >> I don’t have an answer to contribute, but I would be very interested
>>> >> in
>>> >> hearing about experiences in terms of their relative runtime
>>> >> performance.
>>> >>
>>> >> My gut feeling is that an an indirect function call for every (>>=),
>>> >> with many calls to `lift` each time, would make a deep monad
>>> >> transformer stack much more expensive. A free monad approach seems to
>>> >> be more sensible to me. But maybe GHC is doing a better job optimizing
>>> >> this than I would think?
>>> >>
>>> >> So if you have any number-supported evidence about this, possibly from
>>> >> a real-world application where you tried to use one or the other,
>>> >> please share it with us!
>>> >>
>>> >
>>> > There's a paper from Oleg discussing "Freer Monads, More Extensible
>>> > Effects": http://okmij.org/ftp/Haskell/extensible/more.pdf
>>> >
>>> > The conclusion there seems to be that the EE approach is more
>>> > "efficient". But you'll have to look at the concrete performance cases
>>> > and data yourself to make a judgement.
>>> >
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